I suggest you ...

Keep track of "similar items", show them in test mode

Conjugated / inflected forms of words should be kept track of, and should be listed somehow during testing. I test myself for the gender of nouns in the L2 no context mode, with the gender listed as a tag; it would be helpful to have a way to practice conjugation. This feature would also be helpful for languages like Russian to practice declension.

Preferably there would be a specific mode for testing similar items relative to their different tags, ie. you would be given a verb, the interface would ask "what is this word's [infinitive] form", with the value of [x] being determined by the tag(s) that differentiate the word you were given and the word you're being tested on, then show it when you press the space bar.

Perhaps there should also be a way to disable practicing certain tags, so for example in german one might not want to practice the many inflected forms of participles, so that should be disabled. It should also be possible in reading mode to show conjugations/inflections in a table in the definition field.